1. Field of the Invention
This invention relates to a process for the manufacture of urethane group containing polyisocyanurate foams, and more particularly the production of foams produced from polyisocyanates and polyols and (if required) frothing agents, auxiliaries and additives in the presence of a novel co-catalyst system.
2. Description of the Prior Art
The manufacture of polyisocyanurate foams is a familiar process. For this purpose polyisocyanates in the presence of auxiliaries and catalysts are made cyclic and are polymerized. The resulting polyisocyanate group containing isocyanurates and polymerizates are mixed with polyols. Under certain circumstances it is also appropriate to conduct the tri- and/or polymerization and polyaddition of the polyisocyanates and polyols simultaneously.
In the currently available literature numerous catalysts for the cyclization and polymerization are described. To be mentioned as examples are: concentrated bases, such as quarternary ammonium hydroxide, for instance, benzyltrimethylammonium hydroxide, alkaline metal hydroxides, for instance, sodium or potassium hydroxide, alkaline metal alkoxides, such as sodium methylate and potassium isopropylate, trialkylphosphine, for instance, triethylphosphine, alkylaminoalkylphenols, for instance, 2,4,6-tris-(dimethylaminomethyl)-phenol, 3- and/or 4-substituted pyridines, organometallic salts, for instance, tetrakis(hydroxyethyl)sodium borate, Friedel-Crafts catalysts, for instance, aluminum chloride, ferric chloride, boron trifluoride and zinc chloride and alkaline metal salts or weak organic acids and nitrophenolates, for instance, potassium octoate, potassium-2-ethyl-hexoate, potassium benzoate, sodium picrate and phthalimide potassium. Suitable trimerization catalysts are also the strongly basic N,N',N"-tris-(dialkylaminoalkyl)-s-hexahydrotriazine, for instance, the N,N'N"-tris-(dimethyl-3-aminopropyl)-s-hexahydrotriazine and 2,4,6-tris-(dialkanolamino)-s-triazine, such as 2,4,6-tris-(diethanolamino)-s-triazine and mixtures of the listed triazine derivatives.
In addition to the referred cyclization and polymerization catalysts it is often advantageous to add compounds which catalyze the polyurethane formation from polyols and polyisocyanates. Particularly well suited for this purpose are tertiary amines, such as 1,4-diazabicyclo-(2,2,2)-octane and N,N-dimethylbenzylamine, certain organometallic compounds, such as stannous octoate and dibutyltindilaurate and mixtures of tertiary amines and tin compounds.
The drawbacks of the described catalysts are that some of the compounds are difficult to obtain; that the catalysts become effective at elevated temperatures only; that the isocyanurate formation is insufficient or that the tri- and/or polymerization reaction is too slow or too fast, i.e., that the reaction cannot be controlled or be adjusted to local conditions and equipment. The literature does contain information to the effect that the catalysts can be neutralized and the isocyanurate formation can be stopped after a certain degree of polymerization is reached. If basic compounds are used this is accomplished by using inorganic acids, such as hydrochloric acid or phosphoric acid, or organic carboxylic acid chlorides such as benzoyl chloride or acetyl chloride. There is, however, no information as to how system characteristics such as the cream and rise time can be varied during the manufacture of polyisocyanurate foams.
Another drawback of the use of traditional catalysts is that relatively brittle, coarsely pored foams with medium mechanical properties may be obtained, depending upon the type of catalyst used.